Damson is a read-only fan-out replica of Banana. That is, it is a partial replica using one-way LDAP replication.

Eggplant is an updatable fan-out replica of Banana. That is, it is a partial replica using two-way LDAP replication.

If Banana goes down, replication between the multimaster DRG and its fan-out replicas is broken.

An administrator can switch Eggplant and Damson to a new supplier, Candy.

Only two failover topology types are supported:

The consumer and new supplier are both connected to the old supplier with LDAP-based replication agreements. This is shown in Figure 40-2. Node 1 and Node 3 both have LDAP replication agreements with Node 2. Node 2 is the original supplier for Node 1. When Node 2 fails, you can fail over Node 1 to a new supplier, Node 3.

Figure 40-2 Consumer and New Supplier Connected to Old Supplier by LDAP

The consumer is connected to the old supplier with an LDAP-based agreement and the old supplier is in the same Advanced Replication group as the new supplier. This is shown in Figure 40-3. Node 2 and Node 3 are in the same Advanced Replication DRG. Node 2 is the original supplier for Node 4. When Node 4 fails, you can fail over Node 4 to a new supplier, Node 3.

Figure 40-3 Old and New Suppliers in the Same Advanced Replication Group

40.1.1 Limitations and Warnings for Replication Failover

This section describes limitations and warnings related to the use of replication failover.

Following failover, you must compare and reconcile the consumer with the new supplier.

The new agreement must be of the same type and direction as the old agreement.

Only two topology types are supported.

When a supplier fails, its directly connected replica can only fail over to another directly connected replica of the failed supplier.

The replication filtering policy for the agreement between the new supplier and old supplier must match that between the old supplier and consumer.

In most cases, you should fail over the replica in a way that preserves the original replica type. In the case shown in Figure 40-4, node 2 is the old supplier for both node 1 and 3, and node 1 is read-only. When node 2 fails, you could, in theory, set up either node 1 or 3 as the new supplier node. Best practice, however, is to fail over node 1 so that node 3 is the supplier. This preserves node 1's original, read-only replica type.

Figure 40-4 Failover Preserving Replica Type

If the new agreement is a two-way agreement, after you compare and reconcile the consumer with its new supplier, you must also compare and reconcile all other replicas that are connected to the new supplier with the new supplier. For example, in Figure 40-5, Node 2 has a two-way agreement with Node 3. Node 3 is connected to another replica, Node 4. When Node 2 fails, you set up a two-way agreement between node 3 and node 1. After comparing and reconciling node 3 with node 1, you must also compare and reconcile Node 4 with node 3 to ensure that the replicas are synchronized.

Figure 40-5 Compare and Reconcile All Connected Replicas

40.1.2 Determining Which Type of Replication Failover to Use

There are two types of replication failover. They are:

Stateless

Time-based

Use stateless failover when you are unable to plan for the failover in advance. Stateless replication failover makes no assumptions about the state of the replicas. You can fail over to a new supplier at any time. Stateless failover requires more work after failover to synchronize the nodes.

Use time-based failover for planned failover. Time-based failover results in less work after failover. However, it requires some setup ahead of time to ensure that the following assumptions are true at the time of failover:

The nodes are mostly synchronized

The new supplier has preserved its change logs so that complete synchronization can be achieved quickly.

40.2 Performing a Stateless Replication Failover

This section explains how to perform a stateless replication failover. It consists of the following tasks:

40.2.2 Task 2: Break Old Replication Agreement and Set up New Agreement

Break the old replication agreement between the old supplier and consumer and set up a new agreement between the new supplier and consumer. Do this by using the Replication Environment Management Tool. Type:

you are prompted for the source and destination replication dn passwords.

This example assumes that the entire directory is replicated and, therefore, that base is set to " ". If you are using partial replication, use the base and dns2exclude arguments to the oidcmprec tool to include the desired DIT.

40.3.6 Task 6: Break Old Replication Agreement and Set Up New Agreement

Break the old replication agreement between the old supplier and the consumer, then set up a new agreement between the new supplier and the consumer. Do this by using the Replication Environment Management Tool, as follows: